WARNING
These products can expose you to chemicals including Di(2-ethylhexyl)phthalate (DEHP),
which is known to the State of California to cause cancer and birth defects or other reproductive harm.
For more information go to www.P65Warnings.ca.gov

Years ago, high purity water was used only in
limited applications. Today, deionized (Dl) water has become an essential
ingredient in hundreds of applications including: medical, laboratory,
pharmaceutical, cosmetics, electronics manufacturing, food processing, plating,
countless industrial processes, and even the final rinse at the local car wash.

THE DEIONIZATION PROCESS

The vast majority of dissolved impurities in
modern water supplies are ions such as calcium, sodium, chlorides, etc. The
deionization process removes ions from water via ion exchange. Positively
charged ions (cations) and negatively charged ions (anions) are exchanged for
hydrogen (H+) and hydroxyl (OH-) ions, respectively, due to the resin's greater
affinity for other ions. The ion exchange process occurs on the binding sites of
the resin beads. Once depleted of exchange capacity, the resin bed is
regenerated with concentrated acid and caustic which strips away accumulated
ions through physical displacement, leaving hydrogen or hydroxyl ions in their
place.

DEIONIZER TYPES

Deionizers exist in four basic forms:
disposable cartridges, portable exchange tanks, automatic units, and continuous
units. A two-bed system employs separate cation and anion resin beds. Mixed-bed
deionizers utilize both resins in the same vessel. The highest quality water is
produced by mixed-bed deionizers, while two-bed deionizers have a larger
capacity. Continuous deionizers, mainly used in labs for polishing, do not
require regeneration.

TESTING Dl WATER QUALITY

Water quality from deionizers varies with the
type of resins used, feed water quality, flow, efficiency of regeneration,
remaining capacity, etc. Because of these variables, it is critical in many Dl
water applications to know the precise quality. Resistivity/ conductivity is the
most convenient method for testing Dl water quality. Deionized pure water is a
poor electrical conductor, having a resistivity of 18.2 million ohm-cm (18.2
megohm) and conductivity of 0.055 microsiemens. It is the amount of ionized
substances (or salts) dissolved in the water which determines water's ability to
conduct electricity. Therefore, resistivity and its inverse, conductivity, are
good general purpose quality parameters.

Because temperature dramatically affects the
conductivity of water, conductivity measurements are internationally referenced
to 25°C to allow for comparisons of different samples. With typical water
supplies, temperature changes the conductivity an average of 2%/°C, which is
relatively easy to compensate. Deionized water, however, is much more
challenging to accurately measure since temperature effects can approach 10%/°C!
Accurate automatic temperature compensation, therefore, is the "heart' of any
respectable instrument.

RECOMMENDED INSTRUMENTATION

Portable instruments are typically used to
measure Dl water quality at points of use, pinpoint problems in a Dl system
confirm monitor readings, and test the feed water to the system. The handheld
Myron L® Company instruments have been the first choice of Dl water professionals
for many years. For two-bed Dl systems, there are several usable models with
displays in either microsiemens or ppm (parts per million) of total dissolved
solids. The most versatile instruments for Dl water is the 4P or 6PFCEUltrameter II™,
which can measure both ultrapure mixedbed quality water and unpurified water. It
should be noted that once Dl water leaves the piping, its resistivity will drop
because the water absorbs dissolved carbon dioxide from the air. Measuring of
ultrapure water with a hand-held instrument requires not only the right
instrument, but the right technique to obtain accurate, repeatable readings.
Myron L® Company instruments offer the accuracy and precision necessary for
ultrapure water measurements.

In-line Monitor/controllers are generally
used in the more demanding Dl water applications. Increased accuracy is realized
since the degrading effect of carbon dioxide on high purity water is avoided by
use of an in-line sensor (cell). This same degradation of ultrapure water is the
reason there are no resistivity calibration standard solutions (as with
conductivity instruments). Electronic sensor substitutes are normally used to
calibrate resistivity Monitor/controllers.

Myron L® Company manufactures a variety of
in-line instruments, including resistivity Monitor/controllers which are
designed specifically for Dl water. Seven resistivity ranges are available to
suit any Dl water application: 0-20 megohm, 0-10 megohm, 0-5 megohm, 0-2 megohm,
0-1 megohm, 0-500 kilohm, and 0-200 kilohm. Temperature compensation is
automatic and achieved via a dual thermistor circuit. Monitor/controller models
contain an internal adjustable set point, piezo alarm connectors and a
heavy-duty 10 amp relay circuit which can be used to control an alarm, valves,
pump, etc. Available options include 4-20 milliamp output, 3 sensor input, 3
range capability and temperature. Internal electronic sensor substitutes are
standard on all Monitor/controllers.

Sensors are available constructed in either
316 stainless steel or titanium. All sensors are provided with a 3/4" MNPT
polypropylene bushing and 10 ft./3 meters of cable. Optional PVDF or stainless
steel bushings can be ordered, as well as longer cable lengths up to 100 ft./30
meters.

The
following table briefly covers Myron L® Company instruments for Dl water
applications. For details and recommendations, please refer to Myron L® data
sheets, or
Contact us by email
sales@myronl.com.